Characterization and optimization of MIMO systems

In recent years demand for wireless products and networks has experienced substantial growth in the area of digital communications, evolving from novelty into necessity. The deployment has been remarkable in the new generation of IEEE 802.11n-based Wi-Fi technology, which has introduced several enhancements in wireless LAN performance. The most significant innovation has been the introduction of MIMO (multiple-input-multiple-output) interface. MIMO employs an antenna system with multiple transmitters and receivers, improving RF signal quality and increasing efficiency, reliability and throughput. This technology implements advanced signal processing and modulation techniques, added to exploit multiple antennas and wider channels. The potential of MIMO systems bring along several topics. One of these is the choice of design parameters, like, for example, symbol rate, modulation and coding, constellation size and many other. Since the propagation situation can quickly changes, the performance of MIMO systems is determined by its ability to adapt to the changing channel conditions. Thus sophisticated techniques have been proposed to improve the data rate by adapting some of these parameters to the time-varying channel. Another major question is figuring out the ways multiple antennas should be positioned for uncorrelated reception. Due to the fact that antenna elements and propagation channel interact in MIMO systems, the array arrangement strongly influences performance. The configuration has to be chosen carefully with the aim of getting high efficiency in terms of power and a low correlation by exploiting various propagation paths.